Laser light typically has an intensity distribution which is the strongest near its center and gradually becomes weaker toward peripheries as in a Gaussian distribution. However, laser light having a spatially uniform intensity distribution has been desired for laser processing and the like. In this regard, Patent Literature 1 discloses, as a laser light shaping optical system for shaping an intensity distribution of laser light into a spatially uniform intensity distribution, one comprising an aspherical lens type homogenizer. The laser light shaping optical system disclosed in Patent Literature 1 further comprises a transfer lens system (image-forming optical system) immediately behind the homogenizer in order to solve the problem that the laser light emitted from the homogenizer is distorted according to its propagated distance.
On the other hand, it is desirable for laser processing and the like to be able to perform fine processing. When forming a modified layer such as an optical waveguide, for example, converging points are desired to be as small as possible. When the processing position is deeper, however, aberrations (wavefront distortions) cause converging regions to expand, thereby making it harder to keep a favorable processing state. In this regard, Patent Literatures 2 and 3 disclose, as an optical system for correcting aberrations of laser light, i.e., as a wavefront controlling optical system for controlling the wavefront of laser light, one comprising a spatial light modulator (SLM). The wavefront controlling optical system disclosed in Patent Literature 2 further comprises an adjustment optical system (image-forming optical system) between the SLM and a condenser optical system in order for the SLM and the condenser optical system to yield the same wavefront form.